The disperse dyeing of hydrophobic synthetic fibers is normally done by the immersion of the material to be dyed into an aqueous dye bath which contains the dyestuff and various additives and auxiliaries. In this procedure it is important to obtain a reproducible exhaustion of dye from the bath to the material and to obtain a uniform distribution of the dye on the material. This can be done by dyeing at temperatures in excess of 100.degree. C., typically 125.degree. to 135.degree. C. for polyesters and 110.degree. to 115.degree. C. for Qiana.RTM. type polyamides. Naturally such dyeing must be done in pressurized equipment. Alternatively the dyeing can be done at or near the boil, i.e. about 100.degree. C., if large amounts of suitable additives called "carriers," e.g. 10% o.w.g., are added to the dye bath. These additives both accelerate the exhaustion or adsorption by the material of the dye from the bath and at the maximum dyeing temperature promote the uniform distribution of the dye, or levelness. The acceleration feature is necessary in this process because at temperatures near the boil the exhaustion of the dye would be inadequate under acceptable commerical conditions without such acceleration. A process of low or "at the boil" temperature dyeing using aromatic alkyl ethers such as anisol and phenetol as the carrier or "dyestuff adjuvant" is disclosed in French Pat. No. 1,159,581.
For economic reasons the high temperature dyeing procedure has come to be preferred and is largely the method of choice in the United States. However, levelness was found to be a recurrent problem. Attempts were made to solve this problem by the addition of small amounts of traditional carriers, e.g. 1-3% o.w.g. While these additives did promote dye migration which is important to achieving levelness they had an undesirable side effect in this process; they prematurely fixed the dye during the heat-up phase resulting in unlevelness. To avoid this effect it was necessary to either slow down the rate of heating the bath to dyeing tempertures or to spend excessively long times at elevated temperatures to allow the necessary migration of unevenly fixed dye. Thus the acceleration feature of these carriers which was important in the "at the boil" dyeing procedure was an undesirable property in the pressurized higher temperature dyeing procedure.
An additive which would promote dye migration without accelerating the exhaustion of the dye onto the material being dyed would be of interest as a levelling agent.